I haven't had as close a call as that, but I am rather paranoid about other aircraft anywhere near London VORs, especially since GPS now ensures that everybody passes directly over the top of them.
I've been doing most of my flying recently in an aircraft fitted with a Skywatch TCAS system, and it's alarming how many aircraft it alerts me to that I'd simply not been aware of. Even with three or four people looking out it can be impossible to spot another aircraft in spite of knowing it's there and where to look. It's rather sobering, but has its own dangers in that TCAS can lull you into a false sense of security if you forget that there are plenty of aircraft out there without transponders, and a surprising number with transponders either not working or turned off.
This is one area where a healthy dose of paranoia is a good thing